This invention relates to a monitor for a digital transmission line. More specifically, this invention relates to a transmission device which includes the function of monitoring the performance of the transmission line in a transmission system wherein two or more transmission devices are connected via lines. The transmission device may include two or more end offices and two or more intermediate exchanges located between the end offices and perform the function of monitoring the performance of each exchange or cross-connect system, for example, from one end office.
The conventional performance monitor function for measuring data errors in a transmission line during digital transmission is disclosed in JP-A-245827/1987 and JP-A-167161/1984, wherein the performance monitor function is implemented by inserting a performance monitor signal (which includes a CRC value and the like based on a transmission signal from the transmitting end) in monitors that are between transmission devices or switching devices located in the transmission line. The performance monitor signal is extracted on the transmitting end, and the operation value such as the CRC value from the transmission signal and the CRC value of the performance monitor signal received are compared in order to detect errors. Moreover, the performance monitor is independently implemented in monitors existing in the end-to-end monitor section.
In addition, a method of monitoring a combination of arbitrary contiguous units in the monitor section is disclosed in JP-A-163433/1987.
A method checking the result is disclosed in JP-A-245827/1987 and JA-A-167161/1984, wherein the monitor of the result is implemented on the monitor signal transmitting end by inserting the response into a backward signal. Moreover, a performance measurement method is disclosed in JP-A-304046/1992, wherein the performance monitor signal transmitted from the start point to another point is directly returned to the start point and the performance measurement is implemented on the start point. In JP-A-163433/1987, the transmission device which implements the performance monitor by transferring only error occurrence pulses to the centralized monitor station in order to perform centralized error count is disclosed.
The end-to-end communication section of this kind comprises two or more switching devices and the performance monitor supposes the status where lines are connected with these connection devices. When the end-to-end quality of unconnected lines planned to be in service is checked in advance, the conventional transmission device with the performance monitor function implements the performance monitor for every discontiguous monitor section and decides whether the required performance is met based on the performance checking result.
The above-mentioned conventional transmission device with the performance monitor function requires that the performance monitor is implemented in the status where all lines for which the performance monitor is implemented are connected. It is supposed for the unconnected lines planned to be in service that when the end-to-end quality of unconnected lines planned to be connected is checked in advance, the performance monitor is implemented for each monitor section divided by the connection device and checks whether any performance fault has been occurred based on the result. Therefore, it is required in order to obtain the performance checking result in advance that the performance monitor is implemented for each monitor section and the performance checking results for each monitor section are collected and edited to provide performance information among the end-to-end sections.